Fusarium wilt caused by Fusarium udum Butler, is an economically important disease of pigeonpea (Cajanus cajan (L.) Mill). Information on the mechanisms of resistance to this disease in pigeonpea is limited. To study the role of vascular occlusion in wilt resistance, isolates of F.udum were inoculated onto resistant and susceptible varieties of pigeonpea and observed under light and transmission electron microscopes. The presence of F. udum in wilt susceptible plants was characterized by mycelia and conidia in the xylem vessels, plugging in some vessels, disintegration of xylem parenchyma cells in the infected areas, and the formation of cavities due to heavy colonization in the pith cortex vascular bundle. Resistance to F. udum in the roots and stems of wilt resistant plants was associated with low fungal colonization and high occlusion due to tyloses and gels in the xylem vessels. There were significant differences (P = 0:05) in the number of xylem vessels occluded by tyloses in resistant and susceptible plants with a maximum of 22.5% and 8.0% occlusion, respectively. It is probable that tyloses and gels formed as a result of F. udum interaction in wilt resistant plants are part of a resistance mechanism. Key words: Fusarium wilt,cajanus cajan, resistance, tylose, vascular occlusion

Fusarium wilt caused by Fusarium udum Butler, is an economically important disease of pigeonpea (Cajanus cajan (L.) Mill). Information on the mechanisms of resistance to this disease in pigeonpea is limited. To study the role of vascular occlusion in wilt resistance, isolates of F.udum were inoculated onto resistant and susceptible varieties of pigeonpea and observed under light and transmission electron microscopes. The presence of F. udum in wilt susceptible plants was characterized by mycelia and conidia in the xylem vessels, plugging in some vessels, disintegration of xylem parenchyma cells in the infected areas, and the formation of cavities due to heavy colonization in the pith cortex vascular bundle. Resistance to F. udum in the roots and stems of wilt resistant plants was associated with low fungal colonization and high occlusion due to tyloses and gels in the xylem vessels. There were significant differences (P = 0:05) in the number of xylem vessels occluded by tyloses in resistant and susceptible plants with a maximum of 22.5% and 8.0% occlusion, respectively. It is probable that tyloses and gels formed as a result of F. udum interaction in wilt resistant plants are part of a resistance mechanism. Key words: Fusarium wilt,cajanus cajan, resistance, tylose, vascular occlusion

Gum arabic is a natural gum that is obtained from Acacia senegal and A. seyal, two
leguminous trees originating from Africa. Acacias are one of the most common trees in
Africa's semi-arid savannas and A. senegal occurs throughout the Sahel and Sudanese
woodlands, in the Great Rift Valley and into Southern Africa (White, 1983). These trees have
compound leaves with small leaflets, small white to cream colored flowers and form thin
woody pods. Sudan is the dominant producer of gum arabic, accounting for over 80% of …

Fusarium wilt caused by Fusarium udum Butler, is an economically important disease of pigeonpea (Cajanus cajan (L.) Mill). Information on the mechanisms of resistance to this disease in pigeonpea is limited. To study the role of vascular occlusion in wilt resistance, isolates of F.udum were inoculated onto resistant and susceptible varieties of pigeonpea and observed under light and transmission electron microscopes. The presence of F. udum in wilt susceptible plants was characterized by mycelia and conidia in the xylem vessels, plugging in some vessels, disintegration of xylem parenchyma cells in the infected areas, and the formation of cavities due to heavy colonization in the pith cortex vascular bundle. Resistance to F. udum in the roots and stems of wilt resistant plants was associated with low fungal colonization and high occlusion due to tyloses and gels in the xylem vessels. There were significant differences (P = 0:05) in the number of xylem vessels occluded by tyloses in resistant and susceptible plants with a maximum of 22.5% and 8.0% occlusion, respectively. It is probable that tyloses and gels formed as a result of F. udum interaction in wilt resistant plants are part of a resistance mechanism. Key words: Fusarium wilt,cajanus cajan, resistance, tylose, vascular occlusion

Fusarium wilt caused by Fusarium udum Butler, is an economically important disease of pigeonpea (Cajanus cajan (L.) Mill). Information on the mechanisms of resistance to this disease in pigeonpea is limited. To study the role of vascular occlusion in wilt resistance, isolates of F.udum were inoculated onto resistant and susceptible varieties of pigeonpea and observed under light and transmission electron microscopes. The presence of F. udum in wilt susceptible plants was characterized by mycelia and conidia in the xylem vessels, plugging in some vessels, disintegration of xylem parenchyma cells in the infected areas, and the formation of cavities due to heavy colonization in the pith cortex vascular bundle. Resistance to F. udum in the roots and stems of wilt resistant plants was associated with low fungal colonization and high occlusion due to tyloses and gels in the xylem vessels. There were significant differences (P = 0:05) in the number of xylem vessels occluded by tyloses in resistant and susceptible plants with a maximum of 22.5% and 8.0% occlusion, respectively. It is probable that tyloses and gels formed as a result of F. udum interaction in wilt resistant plants are part of a resistance mechanism. Key words: Fusarium wilt,cajanus cajan, resistance, tylose, vascular occlusion

Fusarium wilt caused by Fusarium udum Butler, is an economically important disease of pigeonpea (Cajanus cajan (L.) Mill). Information on the mechanisms of resistance to this disease in pigeonpea is limited. To study the role of vascular occlusion in wilt resistance, isolates of F.udum were inoculated onto resistant and susceptible varieties of pigeonpea and observed under light and transmission electron microscopes. The presence of F. udum in wilt susceptible plants was characterized by mycelia and conidia in the xylem vessels, plugging in some vessels, disintegration of xylem parenchyma cells in the infected areas, and the formation of cavities due to heavy colonization in the pith cortex vascular bundle. Resistance to F. udum in the roots and stems of wilt resistant plants was associated with low fungal colonization and high occlusion due to tyloses and gels in the xylem vessels. There were significant differences (P = 0:05) in the number of xylem vessels occluded by tyloses in resistant and susceptible plants with a maximum of 22.5% and 8.0% occlusion, respectively. It is probable that tyloses and gels formed as a result of F. udum interaction in wilt resistant plants are part of a resistance mechanism. Key words: Fusarium wilt,cajanus cajan, resistance, tylose, vascular occlusion

Fusarium wilt caused by Fusarium udum Butler, is an economically important disease of pigeonpea (Cajanus cajan (L.) Mill). Information on the mechanisms of resistance to this disease in pigeonpea is limited. To study the role of vascular occlusion in wilt resistance, isolates of F.udum were inoculated onto resistant and susceptible varieties of pigeonpea and observed under light and transmission electron microscopes. The presence of F. udum in wilt susceptible plants was characterized by mycelia and conidia in the xylem vessels, plugging in some vessels, disintegration of xylem parenchyma cells in the infected areas, and the formation of cavities due to heavy colonization in the pith cortex vascular bundle. Resistance to F. udum in the roots and stems of wilt resistant plants was associated with low fungal colonization and high occlusion due to tyloses and gels in the xylem vessels. There were significant differences (P = 0:05) in the number of xylem vessels occluded by tyloses in resistant and susceptible plants with a maximum of 22.5% and 8.0% occlusion, respectively. It is probable that tyloses and gels formed as a result of F. udum interaction in wilt resistant plants are part of a resistance mechanism. Key words: Fusarium wilt,cajanus cajan, resistance, tylose, vascular occlusion